According to friends, Loughner was particularly interested in something called lucid dreaming, when people try to take control of their own dreams to manipulate them.

"Lucid dreaming is when a person has not only very vivid dreams, very clear dreams, but they are consciously aware that they are dreaming, and they are able to influence the dreams," said Dr. Gary Schwartz, a professor of psychology and neurology at the University of Arizona.

It's a concept straight out of movies like "The Matrix" and last summer's "Inception," in which characters live out superhuman lives in their sleep.

Stephen Lebarge, founder of the Lucidity Institute, holds dream camps in Hawaii where he trains people in lucid dreaming, helping them to literally live their dreams.

The dream is "the place where you can do anything without external consequences. So it's a place you can safely explore how to live, what to do, what you might want to do," said Lebarge.

Dreamers Can Violate Laws of Physics and Society

According to Lebarge, the first thing many people want to do in lucid dreaming is to violate the laws of physics -- flying like Superman, for instance. The next thing many want to do is break the rules of society, testing taboos of sexuality and even morality without fear of consequences.

But Lebarge says lucid dreamers can also master martial arts, speak in foreign languages, transport themselves anywhere in the world -- living dream lives without limits that seem every bit as real as their waking lives.

Bryce Tierney, a friend of Loughner's, told Mother Jones magazine that the alleged shooter kept a journal of his dreams, and Tierney saw it.

"That's the golden piece of evidence," Tierney told the magazine. "You want to know what goes on in Jared Loughner's mind, there's a dream journal that will tell you everything."

Did Alleged Shooter Loughner Confuse Waking World with the Dream World?

But Tierney told Mother Jones that his friend got in too deep. Like the characters in the movie "Inception," his dream life became more vivid to him than his waking life, which psychologists say is a very real risk.

"For individuals who become not just gifted lucid dreamers but become obsessed with lucid dreaming and prefer lucid dreaming more than regular life, it becomes potentially dangerous to them and society," said Schwartz.